www.neuron.yale.edu

Hi,

Suppose we have a 2-compartment model with different currents in these two compartments. we inject current and measure membrane potential in the first one.

consider this case: we have injected a constant depolarized current, for a specific duration, in the middle of fist compartment

how can we determine,
1- the value of (total/individual) current that reach to second one and depolarize it?

(after some times the feedback current)

2- the value of (total/individual) current coming from second one to the first compartment?


Thanks in advance,

Karlo

Dear Ted,

Thanks for very fast reply!!

When you're not sure about the meaning of something in the Programmer's Reference,
do an experiment that removes the ambiguity. In this case, make a toy model. Calculate
the values by hand. Compare with what you get from ri().

Dear Ted,

please tell me am i right or no?

I have two compartments model, different currents, with following topology

________
| dend[0] |__________
| dend[0] | dend[1] |
|_______|--------------


and forall nseg=3


dose means axial current between to compartments?

thats_karlo wrote:I have two compartments model, different currents, with following topology
________
| dend[0] |__________
| dend[0] | dend[1] |
|_______|--------------

and forall nseg=3

Then it isn't a two compartment model, is it?

Code: Select all

 dend[1] {  ( v(0.16)-.v(0) )/ri(0.16) }

means axial current between to compartments?

Absolutely correct. In that expression, ri(0.16) is the axial resistance between the first
internal node of dend[1] and the node at the 0 end of dend[1]. v(0.16) and v(0) are
the membrane potentials at those nodes. Therefore v(0.16) - v(0) is the voltage gradient
across the axial resistance, and the ratio v(0.16) - v(0) / ri(0.16) is the axial current that
enters the 0 end of dend[1]. This is equal to the axial current that leaves the 1 end of
dend[0].

But what are the units of this current?

Thanks Ted,


1- probably, i should say, we have two sections, with nseg=3, which means 6-compartment,right?

2-I think the unite for axial current is nA, right?

Yours,

Karlo

True and true. Good work, Karlo.

Hello Ted,

Could you please tell me the following formula is a right method to calculate total current that depolarized cell,(in the soma to reach threshold to firing); I=I1+I2+I3, where

I1=(Ionic current+leak current)*area(0.5)/100 // (like Na+/K+, Ca2+,...) in [nA]
I2=(v(0.5)-v(1))/ri(1) // axial current toward to soma
I3=Iinj // injected current


Karlo

That would work, as long as the default section has nseg = 1. If nseg is not 1, you need
to do
totalarea = 0
for (x, 0) totalarea += area(x)
and then change the equation for I1 to
I1=(Ionic current+leak current)*totalarea/100 // (like Na+/K+, Ca2+,...) in [nA]